1. Field of the Invention
The present invention relates to an improved ground flare stack for burning waste combustible gases such as hydrocarbons.
2. State of the Art
In ground flare stacks, it is necessary to supply air required for burning waste gases stably to the burners in a cylindrical stack. The supply of air is made by non-forced draft, and therefore, influence by wind is inevitable. Under a substantially windless condition, flue gas from the combustion ascends inside the stack, and accordingly, air is introduced around the entire circumference of the lower part of the stack. Thus, air is supplied uniformly, and the combustion will continue stably. On the other hand, when it is windy, the stablity of the combustion is significantly affected causing flow turbulence, particularly because of the formation of eddies in the stack by the air stream flowing into the lower part of the stack from the windward side.
If an eddy occurs in the stack, particularly in the vicinity of the burner, the air supply to the burner will be uneven. Further, fresh air supply will be prevented. Thus, incomplete combustion occurs, and certain undesirable results are obtained such as the generation of black smoke and objectionable odor, or a luminous flame burning at the top of the stack.
In case of a very strong wind, air flows even into the top of the stack obstructing air flow into the bottom of the stack. As a result, normal combustion can not be achieved. In an extreme case, flame may shoot out from the air inlet and the lower part of the stack to create a very dangerous situation.
Seeking a way to weaken the influence of wind on the operation of the ground flare stack mentioned above, we made a survey from various view points. We considered the known countermeasures for a ground flare stack which comprises a stack, a cylindrical fence concentrically surrounding the air inlet at the bottom of the stack, a roof extending outward from the stack above the fence, and a louver at the opening between the fence and the roof. The fence will intercept wind so that the wind may not flow into the stack with velocity head, the roof prevents wind from blowing down inside of the fence so as to stabilize the air stream, and the louver straightens the air stream flowing in. It was experienced, however, that the the countermeasures were still insufficient to completely weaken the influence of a very strong wind, and the expected stable burning of the waste gas was difficult to maintain.
Against the wind blowing into the stack from the top thereof, there was invented and proposed (U.S. Pat. No. 3,730,673) a so-called fluidic diode, or truncated conical-shaped baffle which permits upward flow of flue gas discharge, but resists to intrusion of air from the top, at the inside top of the stack. The fluidic diode is useful to some extent. However, the combination of the fluidic diode with the above mentioned roof, fence and louver failed to give a completely satisfactory ground flare stack.
Our further survey revealed the fact that, while the air stream once intercepted by the fence intrudes inside the stack, eddies occur between the fence and the stack below the stack and along the inner wall of the stack. The experimental result showed that occurrence of the eddies could not be prevented even by using the roof and the louver, and that, in the strongest wind, a portion of the air from the windward side which passed between the fence and the stack to reach the bottom of the stack flows under the bottom of the stack and away to the leeward side.